It is known that recycle systems can be configured to produce ethanol as liquid fuel by ethanol-fermentation of carbohydrate and five and six monosaccharide components existing in, for example, rice, bread, noodles, and the like among leftover foods, such as garbage.
The method involves recovering and saccharifying organic wastes containing a source of sugar, such as starch, to obtain monosaccharide, adding ethanol fermentation yeast thereto to consume all monosaccharide for several hours to about several months, and then distilling an ethanol fermented liquid to separate and refine ethanol. In order to obtain the ethanol with a purity of 99% or more, azeotropy or a dehydration membrane is used.
Various methods for producing ethanol from leftover food have been hitherto proposed.
For example, Japanese Unexamined Patent Publication No. 2007-111590(the following Patent Document 1) discloses a method including a step of crushing garbage to form crushed particles, a step of producing a saccharified liquid by adjustment of a concentration of starch of the crushed particles and by addition of a saccharifying enzyme, a step of carrying out alcohol fermentation by inoculation of bacteria of Zymomonas mobilis previously grown into the saccharified liquid to thereby produce a fermentation broth, and a step of recovering ethanol by distilling the fermentation broth. Thus, the method is disclosed which can produce ethanol from the garbage with high efficiency by achieving a conversion ratio to glucose exceeding 45%, and which can recover the ethanol with high efficiency using garbage as a raw material, while contributing to production of the ethanol for addition to gasoline in our country.
Japanese Unexamined Patent Publication No. 2005-65695 (the following Patent Document 2) discloses a method for producing ethanol by fermentation using a raw material containing starch. The method includes a pellet formation step of forming a pellet from the raw material, a saccharification step of obtaining a saccharified pellet by inoculation of green mold into the pellet, and a solid fermentation step of performing solid fermentation by adjusting the water content of a fermentation broth consisting of the saccharified pellet, yeast, and water to 30 to 60% by weight at the start of fermentation. Thus, the method and system for producing ethanol is disclosed which does not eject a waste liquid in the process of producing alcohol by developing a new method and system for producing alcohol using the solid fermentation method.
Japanese Unexamined Patent Publication No. 2006-325577 (the following Patent Document 3) discloses a system including an alcohol producing unit, and a waste liquid processing and utilizing unit. The system has the alcohol producing unit, a saccharification unit, a concentrator, a first fermentor, a distiller, and a dehydrator, and is designed to produce alcohol (alcohol for fuel) from a biomass raw material (garbage). In the saccharification unit, lactic acid is formed by microbes living in the garbage, which lessens pH of a saccharified liquid. In the concentrator, the saccharified liquid is concentrated so as to set the concentration of whole sugar of the concentrated saccharified liquid in a range of 100 g/l to 300 g/l, while setting the pH of the concentrated saccharified liquid to about 4.0 due to the condensation of the lactic acid. Thus, the system is disclosed which efficiently utilizes the garbage, and which can effectively produce the alcohol without necessity of disinfection, pH adjustment, and addition of a nutrient source to yeast even in use of the yeast belonging to Saccharomyces cerevisiae for producing liquors.
The related art methods for producing ethanol disclosed in the above Patent Documents 1 to 3, however, would clog pipes with oil components contained in the saccharified liquid, which leads to the problem of reduction in heat recovery rate of starch contained in garbage.
Further, the related art ethanol recycle utilizes sugar contained in organic wastes as a raw material for ethanol, and thus has the problem that all materials other than sugar are ejected as residues.